1. Field of the Invention
The present invention relates to a primary radiation diaphragm for X-ray examination devices, and in particular to such a radiation diaphragm having at least one pair of diaphragm plates adjustable in opposite directions relative to each other.
2. Description of the Prior Art
A primary radiation diaphragm having two diaphragm plates movable in opposite directions relative to each other for limiting the extent of an X-ray beam is described in German OS 1,800,879. In this known radiation diaphragm, the edges of the adjustable plates are wedge-shaped so that the x-radiation is not completely absorbed by the diaphragm at the region close to the edge thereof. This serves two purposes. First, a good gating of the diagnostically relevant image region is possible, so that substantially no image regions not containing useful image information are bright enough to interfere with viewing of the relevant image. Second, when using a picture reproduction device, such as a monitor, for introducing instruments into the examination subject, it is assured that the instrument can be seen before entry into the diagnostically relevant region.
In this known primary radiation diaphragm, the diaphragm edges limiting the X-ray beam are straight. In practice, such a straight edge does not always correspond to the desired limitation of the image field. Particularly, for gating the regions surrounding the heart, a curved edge contour is desirable so that the image field can be optimally adpated to the shape of the heart.
A diaphragm system having plates with differently shaped edges which can be moved above each other is described in USLP 3,980,407. Different shapes at the gated field can be achieved using the same diaphragm plates in this manner.